Mariachis serenade first lady Jackie Kennedy, left, President John F. Kennedy, Lady Bird Johnson and Vice President Lyndon Johnson at a LULAC dinner at the Rice Hotel in Houston on Nov. 21. 1963, the night before the president was killed in Dallas.

President John F. Kennedy was supposed to just stop by and wave hello.

Instead a group of eager Latinos persuaded him to come inside and speak to a packed room of Mexican-American civil rights activists. And then he persuaded his wife, first lady Jacqueline Kennedy, to address the crowd in Spanish.

It was Nov. 21, 1963. Hours later, the president was dead, his assassination overshadowing the significance of a speech that can be seen as the birth of the Latino vote, so instrumental in 2012 in helping re-elect the first black president, Barack Obama

To historians, Kennedy's appearance at the Rice Ballroom in Houston was likely the first time that a president officially acknowledged Latinos as an important voting bloc.

Though there are no plaques marking the historic occasion, the event is a touchstone for activists.

The surprise visit came after Mexican-Americans in Texas, New Mexico, California, Arizona, Illinois and Indiana helped Kennedy win critical swing states in 1960, thanks to an unprecedented voter registration drive in Latino communities. Independent "Viva Kennedy!" clubs sprang up. Sen. Dennis Chavez, D-N.M., and Texas legislator Henry B. Gonzalezof San Antonio, a future congressman, began speaking in Hispanic neighborhoods across the country and positioned themselves as the first recognizable national Latino political figures.

On Election Day in 1960, Kennedy won 85 percent of the Mexican-American vote.

But during Kennedy's first months in office, Latino leaders expressed dismay that the president had failed to appoint Hispanics in his administration. Chavez even openly criticized Kennedy for his lack of appointments; other leaders embarked on a letter-writing campaign over the slow movement on civil rights.

Sensing another close election in 1964 and hoping to ease tensions, Kennedy visited Texas in November 1963. Advisers suggested that he at least pay a quick visit to Mexican-American activists at a Houston gala sponsored by the League of United Latin American Citizens, then the largest Latino civil rights group in the country.

"The Secret Service told us that he may stop by, but not to advertise it because it wasn't part of his official schedule," said Alexander Arroyos, 76, who was an officer in LULAC at the time. "We could spread it through word of mouth. No one believed us."

Then Kennedy showed up.

He was greeted at the door by Macario Garcia, who was awarded the Medal of Honor for his service in World War II.

Kennedy spoke briefly about foreign policy in Latin America and the importance of LULAC. The first lady told the crowd in Spanish that Texas had a deep history with Latinos. The crowd responded with chants of "Viva Kennedy!"